It is often desired to provide a means of demonstrating products in a consumer/retail environment. This is done in order to facilitate sales demonstrations, and to allow the customer to "play with" the product without the assistance of sales personnel. In the case of a laser printer, the product is designed to be operated by a computer. Computers are often used to demonstrate printers, but the computer tends to add complexity to the demonstration. Additionally, the computer is often costly and distracts from the product. Other disadvantages of the use of a computer are that they are bulky and require additional arrangements for external power.
Some printer products have been provided with an internal demonstration mode. For simple products, such as a typewriter, this can be incorporated into the design at a low cost; however, the extent of data is, limited. In the case of printers having memory expansion capabilities, a "demo SIMM" has been inserted into a memory expansion slot to provide a demonstration function. This has the disadvantage that it requires that the "demo SIMM" be removed prior to sale, and that the customer be shown how to engage the demonstration.
Internal demonstration modes, such as the "demo SIMM", have the disadvantages of: 1) being difficult for the customers to use; 2) "taking over" the machine so that it can no longer operate in its normal mode; 3) requiring the product to have some means of adding the demonstration, such as a memory expansion slot or a font cartridge slot; and 4) the possibility of losing the "demo SIMM" or font cartridge when it is not removed before the machine is sold.
Significantly, some of the assignee's Laser Jet.TM. printers do not have either a memory expansion slot or a font cartridge slot. The use of a demonstration unit which requires either of these would not be possible.
The requirement of a separate power source for external demonstration devices is significant in the retail environment. In addition to requiring additional steps on installation, the availability of a separate power supply may be limited. Connections for a power supply tend to involve costly hardware capable of safely transmitting line voltage at specified current levels. In addition, the use of a power supply means that the demonstration device unit must be certified by the various certification agencies (e.g., Underwriters Laboratories, and the Federal Communications Commission) of the countries in which such a demonstration device is used.
It is also desired to be able to test printers in the field by providing a known external signal to the printer. In doing so, it is desirable to provide such tests separate from external factors, such as the normal driving computer, network connections, etc. Again, it is desired to provide such test signals without the requirement for providing a separate power connection.
The assignee's Laser Jet.TM. laser printers incorporate a Centronics "parallel" I/O port interface which permits direct computer "line port" connections. The Centronics "parallel" I/O interface is the de facto industry standard connector for computer printers. These connections typically do not include a discrete power connection. Another source of power is therefore normally used, should a power supply be necessary, as is the case where it is necessary to supply power to a network adaptor or buffer.
Prior art devices have used power supplies from an RS-232 interface. These include "security keys" for PCs and workstations, and serial mouse units. Both of these applications use a 12 volt supply available from a computer, and do not utilize the regulated V.sub.cc logic level power supply potential, which is normally 3 or 5 volts (although regulated 12 volt potential has in the past been utilized as V.sub.cc). For efficiency and convenience it is desired that a special purpose computer be able to draw its power from the (5 volt) V.sub.cc interface without having specific connections designed to provide the required power, and without having a special accessory connection.
The power consumption of a special purpose computer for demonstrating a printer is used to generate an oscillation signal (power an oscillator), to retrieve and process data and to transmit the data. The initial powering up of the oscillator draws a significant amount of current and therefore would adversely affect a V.sub.cc supply potential. Once powered up, the oscillator uses significantly less current for maintenance and is substantially less likely to adversely affect V.sub.cc.
The Centronics "parallel" I/O port connection includes several terminals which, as an aggregate, can be expected to receive power from the printer's power supply, but are not themselves power connections. It would therefore be desirable to "leech" power, or draw power from these terminals for running a special purpose computer without adversely affecting printer operation by this power draw.
It is therefore desired to provide a special purpose computer which is used as a demonstrator display for a printer, which is readily adaptable to the printer and which is easy to connect with, or disconnect from, the printer. It is desired to provide such a special purpose computer which is able to operate without separate connection to either a power supply or line current. It is further desired to provide such a special purpose computer which is able to provide a desired demonstration in a facile manner.
It is further desired to provide a simple test device for testing a printer or other computer peripheral. It is desired to be able to simply and easily achieve the testing by plugging the test device into the peripheral in order to determine the nature of the peripheral's response to external signals. It is desired to achieve such testing separately from computer connection, and without the requirement that the test device be separately connected to power.